RuboCop Issue 1314 fixed, so Gemfile use restored.

See https://github.com/bbatsov/rubocop/issues/1314 — as expected, it
took me longer to research the bug report than @bbatsov to fix the
actual bug involved. We're baaaaaack!

RSpec: 676 examples, 0 failures (but see Issue #87)
RuboCop: 151 files inspected, no offenses detected